Establishment of a simple and rapid method to screen for strong promoters in Bacillus subtilis

Using published plasmid vectors containing the bgaB gene encoding a heat-stable β-galactosidase, we have been unable to fuse strong promoters to this reporter gene. In addition, we could not analyze the promoter strength by a plate assay. Therefore, we constructed an Escherichia coli–Bacillus subtilis shuttle vector to allow the cloning of strong promoters and their rapid analysis in B. subtilis by plating on X-Gal plates in the presence of the inducer IPTG. We show that the blue color of the colonies reflects the strength of the promoters, which was verified by measuring the β-galactosidase activities.